Low-Threshold Buprenorphine in Non-Traditional Settings: A Scoping Review

Abstract

Background:

Despite the continuing opioid overdose crisis, the majority of those diagnosed with opioid use disorder (OUD) are not engaged in treatment due to various barriers. Low-threshold buprenorphine programs are designed to reduce treatment barriers. Key tenets of these programs are a harm reduction approach, same-day entry, flexibility, and accessibility. The development of novel programs has expanded low-threshold treatment into mobile units, syringe service programs, and community centers.

Objective:

This scoping review aims to describe approaches taken by programs in non-clinical settings by identifying key components of delivery models, implementation barriers and facilitators, and outcomes. Given the diverse nature of the literature on these programs, a scoping review was selected to review outcomes and to identify gaps.

Methods:

A protocol following the PRISMA-ScR guidelines was developed to systematically search 5 databases: Medline, Embase, CINAHL, PsycInfo, and Web of Science. Articles published prior to January 31, 2024 that described buprenorphine programs operating outside traditional healthcare settings were included.

Results:

The search identified 18 784 articles, including 147 in full-text review, with 41 meeting eligibility criteria. Common program types encompassed syringe service, mobile, community center, and street medicine. All programs emphasized community partnerships as key implementation facilitators and noted funding is urgently needed.

Conclusion:

Low-threshold buprenorphine programs are an innovative way to deliver OUD treatment to people who otherwise may not have access to and/or engage in treatment. Future efforts should determine which outcomes are most important to people who use drugs, standardize outcome measurements, and implement programs tailored to help communities meet those outcomes.

Introduction

The U.S. Department of Health and Human Services declared the ongoing opioid epidemic a public health emergency in 2017. ¹ In 2022, 6.1 million people in the U.S. had an opioid use disorder (OUD), affecting 2.2% of the population over the age of 12. ² The number of opioid-involved overdose deaths has risen dramatically in recent years, climbing from 47 600 in 2017 to 81 806 in 2022. ³ The epidemic is not restricted to the United States: globally, an estimated 60 million people engaged in non-medical opioid use in 2021, 1.23% of the world population aged 15 to 64. ⁴ Expanding access to medications for opioid use disorder (MOUD) has transformed the treatment landscape, as MOUD is demonstrated to increase treatment engagement and retention while decreasing overdose rates, illicit opioid use, all-cause hospitalizations, all-cause mortality, and opioid-related mortality.^5-7 The number needed to treat with buprenorphine to prevent 1 death per year after overdose (52.6) is lower than most commonly-prescribed medications. ⁸ Additionally, one meta-analysis found all-cause mortality decreased by half with engagement in buprenorphine or methadone treatment. ⁹

Despite the efficacy of MOUD, there are still many barriers to treatment access, as only 22% of adults in the U.S. with an OUD received any kind of MOUD in 2021. ¹⁰ Some of these barriers result from controlled substance prescribing regulations. For example, methadone is only available through strictly regulated opioid treatment programs (OTPs). Until 2022, providers in the U.S. were legally required to obtain an “X-waiver” to prescribe buprenorphine and were limited to 30 patients in the first year. Other prescribing barriers exist at the insurance and pharmacy levels. While most insurers cover at least 1 buprenorphine formulation, extended-release injectable buprenorphine is often considered non-formulary and additional requirements such as prior authorizations and quantity limits are common. ¹¹ Once insurance coverage has been assured, clients may find their preferred pharmacy does not carry buprenorphine. Among U.S. counties with greater-than-average opioid-related mortality, 1 in 5 pharmacies indicated they do not dispense buprenorphine, according to an analysis of randomly selected pharmacies. ¹²

Other barriers stem directly from the healthcare system. These include but are not limited to long wait times, restricting intake hours, not allowing distribution of buprenorphine/methadone on the first visit, requiring in-person dosing (especially at OTPs), strict restrictions on maximum dosage or time in treatment, requiring clients to participate in counseling, requiring frequent urine drug tests, and/or mandating abstinence from all substances. ¹³ Clients often experience stigmatizing events when they interact with the healthcare system, which erodes trust in traditional healthcare settings.^14,15 Low-threshold treatment models seek to reduce barriers and build treatment programs that better address the needs of the people who access their services. Due to legal restrictions surrounding methadone, low-threshold programs in the U.S. almost exclusively utilize buprenorphine.

Jakubowski and Fox ¹⁶ synthesized prior low-threshold approaches and defined a low-threshold buprenorphine model as including 4 overarching principles: (1) a harm reduction approach, ¹⁷ (2) same-day treatment entry, (3) flexibility, and (4) wide availability in places frequented by people with opioid use disorder. A harm reduction approach generally encompasses operating in a non-stigmatizing, welcoming environment, not stopping treatment due to opioid or other substance use, and working toward patient-centered goals such as reduced overdose risk or use reduction. ¹⁶ Most low-threshold buprenorphine programs have been implemented in primary care and hospital settings. Even so, models are wide-ranging, including emergency department bridge programs, ¹⁸ mobile clinics, ¹⁹ telemedicine,^20,21 and coordination with both syringe service programs, and clinics focusing on the Hepatitis C Virus (HCV). ²² Additionally, the literature on low-threshold programs can be challenging in that not all programs explicitly state their low-threshold approach, but rather imply it by their description, and what is considered low-threshold has evolved throughout the years. In light of the literature’s heterogenous nature, we considered program context, and the programs’ definitions of what is low threshold for inclusion into this review. Finally, as compared to standard, high-threshold approaches, results for low-threshold treatment are promising with higher initiation, ²³ increased buprenorphine adherence among retained participants, ²⁴ and similar retention rates. ²⁵

There is significant potential in developing low-threshold programs in non-traditional settings outside of primary care clinics or hospitals. One cost-effectiveness model of low-threshold buprenorphine in syringe service programs predicted a 20% decrease in fatal opioid-involved overdoses. ²⁶ Low-threshold programs in non-traditional settings may be particularly effective for reaching people with OUD who are not otherwise engaged with the healthcare system. Many such clients express a preference for receiving care in environments perceived as less judgmental and stigmatizing, such as programs operating out of a mobile unit. ²⁷ Despite the promise of these low-threshold programs within existing, non-clinical infrastructures, multiple barriers hinder their development, such as staff training, limited financial support, and appropriate medical provider placement. ²⁸

This scoping review seeks to identify key characteristics, measurement methods, and outcomes of low-threshold buprenorphine programs operating in non-traditional settings. Given the diverse nature of the literature describing these programs, a scoping review was selected rather than a systematic review to identify knowledge gaps and provide a scope of the literature. ²⁹ This study seeks to describe the approaches taken by these programs, elements of their delivery models, obstacles and support during implementation, measures of success, and reported outcomes.

• Question 1: What models of low-threshold buprenorphine care have been developed for non-traditional settings?

• Question 2: What are the key components of these low-threshold buprenorphine models of care?

• Question 3: What determinants of implementation (barriers and facilitators) have been described for these models of care?

• Question 4: What service and clinical outcomes have been associated with these models of care?

Methods

Protocol

Prior to conducting this scoping review, a protocol was developed based on the PRISMA-SCR guidelines. ³⁰ This protocol is registered and on Open Science Framework at https://osf.io/7rshq

Sources of Evidence

Peer-reviewed articles focused on low-threshold buprenorphine treatment programs in non-traditional settings were included in this review while conference abstracts, reports, and dissertations were excluded.

Population, Concept, and Context: Inclusion and Exclusion Criteria

Given the broad range of opioid use disorder treatment programs described in the literature, the following inclusion/exclusion criteria were developed to focus the review.

Participants

Inclusion

Programs providing care to adult or adolescent clients (ages 15 and older) with opioid use disorder.

Exclusion

Programs primarily providing care to clients under age 15.

Concept

Inclusion

Low-threshold or low-barrier programs providing medication for opioid use disorder (MOUD) in the form of buprenorphine.

Exclusion

Given the evolving landscape regarding telehealth-based delivery methods, exclusively telehealth-based programs were excluded. Additionally, as the review seeks to focus on highlighting novel, sustainable settings that can provide buprenorphine treatment directly, rather than initiating treatment or bridging into traditional programs, programs that did not provide ongoing buprenorphine care were excluded. Both telehealth and bridge programs have been recently reviewed elsewhere.^31-33

Context

Inclusion

Community-based programs operating outside traditional health and substance use disorder care settings.

Exclusion

Programs where care had previously been established generally: those operating in a hospital, outpatient primary care clinic, federally qualified health center, or jail/prison.

Search Methods

A search of literature databases was performed in Medline (via PubMed), Embase (Elsevier), CINAHL (via EBSCO), PsycInfo (ProQuest), and Web of Science (Clarivate). Source selection was made based on recommendations by Brahmer. ³⁴ All dates were searched through January 31, 2024. Search string vocabulary terms were grouped into 2 concepts: (1) buprenorphine and its drug synonyms and (2) opiate addiction treatment including safe supply, harm reduction, low-barrier/low-threshold, and medication-assisted treatment. Full search strings, reported in Supplemental Appendix A, were developed with the assistance of the search string development tool created by Brunskill. ³⁵ Covidence software was used for citation screening and data extraction (Veritas Health Innovation, Melbourne, Australia, www.covidence.org).

Selection of Sources of Evidence

Abstracts identified through the described search were imported into Covidence and duplicates were removed. Titles and abstracts were screened independently by 2 reviewers, and any conflicts between the 2 reviewers were resolved by a separate reviewer. Next, full text review was completed by 2 independent reviewers, with a third reviewer resolving conflicts based on the previously defined protocol. Articles not meeting the above inclusion criteria were excluded.

Data Extraction

A team of reviewers developed a data extraction template in Covidence to address the study questions. Extracted data included: (1) article title and first author; (2) total number of participants and participant details (age, gender, race/ethnicity, substance use history, prior treatment attempts, co-morbid conditions); (3) study location, aim, design, start/end dates, funding sources, and conflict(s) of interest; (4) program name and components including type of program, setting (city and type of non-traditional program), treatment entry, harm reduction approach, flexibility, staffing, participant engagement, type, dose, and range/duration of medication provided, requirements for participation (including management of those not meetings program goals), urine drug screen usage, telehealth inclusion, additional services provided, implementation barriers and facilitators, program outcomes (service and clinical outcomes, retention in care, qualitative outcomes), and adverse events; and (5) this study’s inclusion/exclusion criteria. These data points were selected to provide a broad overview of the types of programs, services provided, and implementation facilitators and barriers associated with programs.

Data regarding implementation facilitators and barriers in included articles were extracted using a structure based on the Consolidated Framework for Implementation Research (CFIR). ³⁶ CFIR is a practical framework developed to guide systematic assessment of barriers and facilitators to implementation, categorizing these factors by domains (innovation, inner setting, outer setting, individuals, and implementation process). Based on these domains, data were extracted by 2 independent reviewers then consolidated by a third reviewer. The full spreadsheet of extracted data can be found in Supplemental Appendix B.

Results

Included Studies

A total of 41 articles met criteria and were included in this scoping review.^{18,19,22,24,28,37-72} The PRISMA flow diagram provided in Figure 1 details inclusion and exclusion decisions. Figure 2 details the types of articles included. Of these, 35 were based in the United States, 2 in Canada, 2 in the United Kingdom, 1 in Norway, and 1 in India. Most studies in the U.S. occurred in urban communities, most commonly in Baltimore, MD, and Philadelphia, PA. The following results are organized to respond to each of the review’s 4 guiding questions.

Figure 1.

PRISMA flow diagram of the study selection process. Each of the identified studies were screened, retrieved, assessed for eligibility, and examined by 2 independent reviewers.

Figure 2.

Included Studies. Retrospective chart reviews were most frequently deemed as acceptable to include, followed by qualitative research studies.

Models of Low-Threshold Buprenorphine Care in Non-Traditional Settings

We reviewed the following aspects of the identified program models: location/setting, buprenorphine prescribing and dispensation modalities, and target population. In terms of program setting, the programs described in the 41 included articles can be largely categorized into 4 groups: syringe service programs (SSP), mobile programs, community centers, and street medicine.

Regarding prescribing and dispensation modalities, the ability to prescribe and/or dispense buprenorphine was added to these programs’ existing services in most cases. Other program designs included pharmacy-based programs,^47,56 an integrated obstetric/addiction clinic, ⁴¹ and a medication delivery program designed to reach people living in shelters. ⁶² Thirteen of the 41 programs did not detail how buprenorphine was prescribed or dispensed to patients. Of the 28 that provided details, 8 dispensed buprenorphine directly to patients while 21 provided buprenorphine prescriptions for the patients to fill later at a pharmacy. While initial prescriptions were typically for 1 to 2 weeks of medication, there were dosing inconsistencies with the starting dose ranging from as little as 2 to 16 mg^24,37 and the maximum dose ranging from 16 to 32 mg. ⁶⁴ One program specifically offered micro-dosing regimens to enable same day induction. ⁶⁷

Lastly, the primary target population for each program was individuals with OUD and other substance use disorders. Many programs focused on unique subpopulations, particularly those experiencing homelessness. A few programs targeted even more specific populations, such as individuals involved in the criminal legal system, ⁵⁴ women experiencing homelessness, ⁶⁶ and sex workers. ⁴⁶

Components of Low-Threshold, Non-Traditional Models of Care

The vast majority of the 41 programs included all 4 overarching principles of low-threshold buprenorphine care as outlined previously in Jakubowski and Fox. ¹⁶ Namely, all of the 41 programs utilized a harm reduction approach, 85% (35 yes, 1 no, 5 unknown) had the option of same-day treatment entry, 83% (34 yes, 1 no, 6 unknown) incorporated flexibility into their care, and 83% (34 yes, 1 no, 6 unknown) were located in places frequented by people with opioid use disorder. Program descriptions and other key components are included in Table 1, with additional qualitative themes highlighted in Supplemental Table 1.

Table 1.

Program Descriptions Final. ⁶² .

Types of program	Program type	Study name	Location	Study design & dates	Program description and target population	How medication is provided/dosage	Additional notes
Syringe service program	Harm Reduction Coalition (HRC)	Stancliff 2012	New York City, NY, USA	Cohort study, November 2005 to July 2008	Clients referred by SSP; Target population: marginalized populations, younger clients, long-term heroin use, no prior treatment history	Prescriptions provided; average daily dose 16 mg; 1 wk initial Rx
	Stepped Treatment and Engagement Program (STEP)	Tringale 2015	Los Angeles, CA, USA	Non-randomized experimental study, dates not specified	Pilot study; enrolled clients of the SSP with current heroin use	Buprenorphine directly dispensed twice weekly; doses not specified	Pilot study; self-described as low-threshold but with did require counseling/frequent visits
	Stabilization, Treatment, and Engagement Program (STEP)	Bachhuber 2018	Philadelphia, PA, USA	Retrospective chart review, October 2011 to August 2014	Low-barrier buprenorphine treatment integrated into an SSP	Prescriptions provided; average daily dose 16 mg; 1 wk initial Rx and can space to 4 wk
	King County Public Health Syringe Services Program	Hood 2020	Seattle, WA, USA	Retrospective chart review, 2017 to 2018	Low-barrier buprenorphine treatment integrated into an SSP	Prescriptions provided and can be dispensed from co-located pharmacy; initial 3-4 d supply, can be increased to 1-2 wk once dose is stable
	Homeless Health Care Los Angeles (HHCLA) clinic	Tringale 2021	Los Angeles, CA, USA	Descriptive/implementation study, January 2020 to June 2020	Designed to reach high-risk population during COVID-19; developed telephone booth model to allow for social distancing; target population was clients of syringe service program	Initially majority of patients (86%) were directly dispensed buprenorphine; eventually switched to prescription via coordinated pharmacies	Describes adaptations during COVID: telephone booth development and partnership with pharmacies to coordinate buprenorphine prescriptions
	Safe Recovery	Del Pozo 2022	Burlington, VA, USA	Case Report, 2017 to 2020	Low-threshold buprenorphine provided by city’s syringe service program to clients seeking treatment for OUD	Prescriptions provided	Led by the police department but not enforcement-oriented; focused on harm reduction
	Unnamed	Jakubowski 2022	New York City, NY, USA	Retrospective chart review, February 2019 to October 2020	SSP-based low-threshold buprenorphine treatment program to engage people with opioid use disorder who may be reluctant to seek treatment elsewhere	Prescriptiosn provided; daily dose 16 mg; 1 wk initial Rx
	Unnamed	Jakubowski 2022	New York City, NY, USA	Qualitative research, April 2019 to November 2019	SSP-based low-threshold buprenorphine treatment program to engage people with OUD who may be reluctant to seek treatment elsewhere	Prescription typically given for 1-2 wk, could progress to monthly once patients were stabilized	Describes 6 low-threshold buprenorphine programs in NYC: stage of development, location, availability, provider, SSP staff, documentation, urine toxicology testing
	The Mountain Center	Gadomski 2023	Espanola, NM, USA	Descriptive study, August 2020 to August 2021	Full spectrum care for people with opioid use disorder integrated in harm reduction site	Prescriptions provided
	ANCHOR	Hill 2022	Washington DC, USA	Cohort study, May 2017 to May 2018	Buprenorphine clinic co-located with Hepatitis C treatment clinic	Initial prescriptions 16 mg/d for 1 wk, spaced out per physician discretion	Offered legal support, laundry, showers, community lunch
Mobile Program	New Jersey Medication Assisted Treatment Initiative	Hall 2014	New Jersey, USA	Retrospective chart review, January 2008 to September 2010	Mobile vans that provided buprenorphine and methadone; 6 state-funded sites in different NJ municipalities; 5 had mobile medical units and 1 had an office-based program with a passenger van to transport clients to the office	Not specified	Only 25% of clients chose buprenorphine, remainder were treated with methadone
	Project Connections at Re-Entry (PCARE)	Krawczyk 2019	Baltimore City, MD, USA	Retrospective chart review, November 2017 to November 2018	A mobile low-threshold buprenorphine program located outside of Baltimore City Jail; designed to reach recently incarcerated individuals but sees anyone from the community	Prescriptions provided; dose up to 16 mg/d, initial Rx 2-7 d
	Project Connections at Re-Entry (PCARE)	Selitsky 2023	Baltimore, MD, USA	Retrospective chart review, January 2021 to July 2021	A mobile low-threshold buprenorphine program located outside of Baltimore City Jail; designed to reach recently incarcerated individuals but sees anyone from the community	Prescriptions provided; dosage of buprenorphine varies across patients (up to 32 mg/d); initial Rx up to 1 wk, can space to 4 wk	Study examines retention rates at higher vs lower buprenorphine doses and found higher retention with higher doses
	British Columbia Ambulance Services	Scheuermeyer 2019	Vancouver, Canada	Retrospective chart review, December 2016 to March 2017	Ambulances could bring patients to a specialized trailer for opioid use disorder treatment rather than an emergency room	Medications (methadone and buprenorphine) are prescribed and dispensed; take home doses of buprenorphine with follow up next day for new starts; methadone given for 3 d	Outreach team available and helps with resources
	Community Care in Reach Mobile Health Initiative	Regis 2020	Boston, MA, USA	Mixed methods evaluation, January 2018 to December 2019	Seeks to engage individuals with opioid use disorder not currently in care; staffed by clinician with expertise in caring for individuals experiencing homelessness and harm reduction specialists	Prescriptions provided; observed induction on the first day of treatment	Mixture of street outreach and mobile care
	Safe Healthy Empowered (SHE) clinic	Stewart 2020	Seattle, WA, USA	Retrospective chart review, July 2018 to October 2018	Program designed to reach women experiencing homelessness; served patients with high rates of homelessness, individuals engaged in sex work; provided wraparound care which included buprenorphine for opioid use disorder when needed	Not specified
	Access, Harm Reduction, Overdose Prevention, and Education (AHOPE)	Fine 2021	Boston, MA, USA	Qualitative research, December 2019 to March 2020	Mobile outreach program offering harm reduction services, primary care, and addiction treatment	Prescriptions provided	Offered escort to pharmacy for clients
	Begin the Turn	O’Gurek 2021	Philadelphia, PA, USA	Retrospective chart review, July 2019 to December 2019	Low-barrier, multidisciplinary mobile care unit targeting fatal overdose hot spots	Prescriptions provided; 1 wk initial Rx, can space to 4 wk pending progress and UDS results
	The Spot	Grieb 2022	Baltimore, MD, USA	Qualitative study embedded into a cluster randomized trial, March 2019 to October 2019	Mobile van-based program co-located with SSP vans, offering an array of services including buprenorphine-based MOUD	Prescriptions provided; 1 wk supply	Offered overdose prevention and response training, health insurance enrollment
	The Spot	Rosecrans 2022	Baltimore, MD, USA	Cohort study, September 2018 to November 2019	Mobile van-based program co-located with SSP vans, offering an array of services including buprenorphine-based MOUD	Prescriptions provided; 1 wk supply
	Prevention Point Philadelphia (PPP)	Lowenstein 2023	Philadelphia, PA, USA	Qualitative research, July 2021 to December 2021	Multiple mobile, low-barrier buprenorphine programs designed to increase treatment access among marginalized individuals at high risk of overdose	Prescriptions provided; max dose 24 mg/d; generally 1 wk Rx	Interviews with patients of the mobile units
	Prevention Point Philadelphia (PPP)	Stewart 2023	Philadelphia, PA, USA	Qualitative research, May 2022 to August 2022	Participants of the research were leaders of 7 mobile units that provideor link to MOUD and were in operation in Philadelphia County as of February 2022	Practice varies across mobile units, some prescribe and some dispense medications	Interviews with leaders of 7 different mobile units
	Community Outreach Intervention Projects (COIP)	Messmer 2023	Chicago, IL, USA	Retrospective chart reviewy, July 2021 to June 2022	Mobile medical unit integrated into community-based harm reduction organization targeting opioid overdose hot spots in Chicago, offering primary care and low-threshold buprenorphine	Prescriptions provided; dispensing model under development	Offering post-use monitoring with buprenorphine initiation
	Road to Care	Pepin 2023	Worcester, MA, USA	Community case study, May 2021 to April 2023	A mobile team rooted in emergency medicine and family medicine for patients with opioid use disorders who may also be experiencing homelessnes	Not described
	Communities that HEAL (Helping to End Addiction Long-term) intervention	Chatterjee 2024	Massachusetts and Ohio, USA	Qualitative research, August 2022 to January 2023	Mobile units that provide same-day access to MOUD prescriber at an outreach site, either in-person or via tele	Not specified, “traditional induction” vs low-dose induction (site dependent)
	Prevention Point Pittsburgh	Fixler 2024	Pittsburgh, PA	Quasi-experimental study, January 2018 to September 2022	Four low-threshold buprenorphine mobile vans colocated with a mobile SSP	Prescriptions provided	Examines impact of mobile units on neighborhood arrest rates
	The Great Circle Mobile Medication Unit (MMU)	Hoffman 2024	Grande Ronde, Oregon, USA	Qualitative Research, February 2023 to March 2023	Dispenses methadone or buprenorphine from a mobile van on the lands of the Confederated Tribes of Grande Ronde; target population is American Indian/Alaskan Native communities	Medications dispensed from the mobile unit	Only known Tribally operated mobile medical unit in the United States
Community center/clinic	Unnamed	Tay Wee Teck 2021	Scotland	Case series, March 2020 to October 2020	Self-described low-threshold drop-in program with assertive outreach; describes cases of patients with OUD who wished to transition to injectable buprenorphine and for whom conventional induction were unlikely to be tolerated	Medications dispensed and administered on site; range of micro-dosing regimen start to first injectable buprenorphine is 8-19 d; prescription length varied depending on the point in the program but goal to reach monthly visits	Participants were provided a micro-dosing regimen to enable same day induction of oral buprenorphine; case series of 5 individuals
	Project ORCHID (Organised Response for Comprehensive HIV Interventions in the Districts of Nagaland and Manipur)	Armstrong 2018	Manipur and Nagaland, India	Retrospective chart review, May 2006 to December 2007	Buprenorphine treatment program based in community drop in centers for people who inject drugs	Averaged daily dose varies among the drop in centers
	Project Connections Buprenorphine Program (PCBP)	Truong 2019	Baltimore, MD, USA	Qualitative research, February 2017 to June 2017	Clinic located at peer recovery center in Baltimore that hosts peer recovery meetings and offers referrals/supports	Not described	Program is largely focused on peer support
	Respectful, Equitable Access to Compassionate Healthcare (REACH)	Kapadia 2022	Ithaca, NY, USA	Qualitative research, dates not specified	Harm-reduction based, low-threshold, nurse-led model of buprenorphine therapy in a community-based medical practice	Not described
	Unnamed	Oles 2022	New Haven, CT, USA	Qualitative research, April 2017 to December 2017	Private, community based non-profit organization that primarily treats those who are underinsured or uninsured	Not described
	RAAM (Rapid Access Addiction Medicine) model	Corace 2023	Ontario, Canada	Retrospective chart review, October 2017 to October 2019	RAAM model integrates pharmacologic treatments, psychosocial and behavioral treatments, addiction medicine, and primary care into 1 team to address substance use issues	Prescriptions provided for buprenorphine; methadone referrals offered
	Forward Leeds	Gittins 2023	Leeds, United Kingdom	Cohort study, March 2021 to February 2022	Program designed to reach individuals engaged in sex work in Leeds with a focus on informed choices about buprenorphine prolonged-release injection	Not specified
Street medicine	Low Threshold Substitution Treatment in Oslo	Henriksen 2018	Oslo, Norway	Retrospective chart review, September 2010 to December 2016	Daily free, supervised buprenorphine offered from a street clinic	Daily observed doses dispensed directly from program. Initial dose 4 mg, up to 16 mg.
	San Francisco Street Medicine	Carter 2019	San Francisco, CA, USA	Retrospective chart review, November 2016 to October 2017	Low barrier buprenorphine program with the primary goal of engaging and retaining people experiencing homelessness with OUD in care	Prescriptions provided; typical initial dose of 16 mg/d; initial Rx for 3-7 d
	The Connecticut Mental Health Center	Gibson 2023	New Haven, CT, USA	Retrospective chart review, July 2019 to April 2021	Provides care to unsheltered individuals; offering buprenorphine for those who wanted to reduce their opioid use.	Prescriptions provided; initial 1 wk Rx, can space to 30 d supply
Other: Pharmacy-based	unnamed (pharmacy integrated)	Green 2023	Providence, RI, USA	Feasibility pilot study, February 2021 to April 2022	Prescribers allowed to delegate evaluation and some treatment decisions to pharmacists; pharmacists see patients in the pharmacy and dispense buprenorphine; patients recruited through self-referral, emergency department outreach, or community outreach	Medications dispensed from pharmacy; dose 4-24 mg/d; initial Rx 3-7 d supply, can space to 2 wk
	unnamed (pharmacist outreach program)	Ly 2024	San Francisco, CA, USA	Retrospective chart review, August 2022 to November 2022	Pharmacist-led outreach pilot program to provide buprenorphine treatment to individuals residing in permanent supportive housing	Prescriptions provided; different dosing protocols offered; 1-2 wk Rx	Pharmacist led outreach program
Other: Integrated Obstetric/Addiction clinic	Obstetric/Addiction Clinic	Ellis 2023	Virginia, USA	Retrospective chart review, June 2019 to June 2021	Pregnancy-to-postpartum services provided alongside buprenorphine treatment	Prescriptions provided; mean daily dose 18.5 mg/d	Offered prenatal care, NOWS education, anesthesia birth pain management consultation, lactation consultation, group therapy
Other: Medication delivery to patients in shelters	Community Behavioral Health Services Pharmacy	Samuel 2022	San Francisco, CA, USA	Case series, Fall 2020	Developed to delivery buprenorphine to patients who have residence at a shelter in place (SIP) hotel for homeless individuals in San Francisco	Prescription either delivered by pharmacy staff or picked up at pharmacy	Program offered the ability to personalize prescription delivery to accommodate patient’s schedule

Many programs provided additional services, the most common being general harm reduction support (ie, fentanyl test strips, education, supplies, naloxone kits) (83%), naloxone distribution (51%), referrals to additional services (51%), such as Federally Qualified Health center care, ⁴⁴ urgent and primary care, ²⁴ and bridge clinics, ³⁹ and syringe exchange (44%). The program described in Ellis et al provided prenatal care, anesthesia-birth pain management consultation, and lactation consultation. ⁴¹ Another program provided overdose prevention, response training, and assistance with health insurance enrollment. ⁴⁸ Other services, as described in Samuel et al, included legal case work, access to laundry and showers, community lunch, and prescription delivery. ⁶²

No client participation requirements were specified for 29 of the 41 programs. Nine programs required drug testing, typically through a urine drug test. Of these 9 programs, 5 explicitly stated that drug testing was required at each appointment, whereas the frequency of drug testing for the remaining 4 was unspecified. Bachhuber et al had an orientation with a case manager upon enrollment, ⁷² but the remaining principles were described as low barrier. Another program, Tringale et al, required participation in a peer support group as part of the pilot program but was self-described as utilizing a low-threshold approach. ⁶⁹

We also evaluated what was offered to program clients not progressing in their treatment goals. Of the 41 reviewed programs, 25 did not specify protocols for supporting clients who do not meet goals. Twelve programs referred clients to healthcare providers offering different treatment modalities or more individualized care (eg, methadone programs, inpatient/intensive outpatient programs, FQHC/primary care). Hill et al required 3 consecutive days of directly observed therapy for clients with 2 consecutive urine screens that were negative for buprenorphine; otherwise, they were discharged from the program. ²² If a client missed an appointment in the program described in Tay Wee Teck et al, the client was offered re-initiation into treatment. ⁶⁷

For clients not meeting treatment goals, another 5 programs offered multiple next-step options, often determined by provider discretion or client preference. For instance, the STEP program (Stabilization, Treatment, and Engagement) noted an expectation of cessation of heroin use within 4 weeks of treatment initiation, monitored by urine screens each visit. ⁷² A client still using heroin at week 3 was evaluated for either intensified treatment or increased buprenorphine dosage. ⁷² Some programs prompted clients not meeting goals to either demonstrate dosing(s),^25,37 or increase the frequency of their provider visits.^24,57,72 Approximately one-third of studies noted referring those not meeting treatment goals to alternative programs for further treatment.

Determinants of Implementation

Barriers and facilitators of program implementation are presented in Table 2 and discussed separately below.

Table 2.

Barriers and Facilitators to Program Implementation. Key barriers and facilitators to program creation and execution were identified across settings.

Barriers to implementation
Outer setting	Inner setting	Individual
System/intrastructure gaps	Limited physical space	Stigma on an individual level toward health care or MOUD
Community resistance	High costs	Financial stability
Criminal legal system rules around probation and parole	Staff recruitment and retention	Socioeconomic challenges faced by participants
Stigma toward MOUD	Limited scope of services	Communication challenges (lack of phones) for participants
Insufficient reimbursement rates	Competing treatment philosophies	Lack of insurance for participants
Lack of available funding options
Regulations regarding prescribing/dispensing buprenorphine
Inclement weather (for mobile or street medicine programs)
Facilitators to implementation
Outer setting	Inner setting	Individual
Support from community leaders	Co-location within existing programs	Range of staff experience
External funding	Mobile programs able to travel to meet participants and community partners	Involving peers/PLE
Partnerships with local governments	Utilizing existing physical infrastructure & staff	Staff are reflective of communities being served
Supportive partnering organizations (such as pharmacies)	Partnering with harm reduction programs	Patient referrals/word of mouth
Supportive local criminal legal system

Barriers to Implementation

External Barriers to Implementation

At a systems level, the lack of an appropriate public health infrastructure to guide program development was a challenge in Del Pozo et al. ⁴⁰ Funding was a significant barrier in Kapadia et al, as Medicaid or Medicare reimbursements were often insufficient to support costs. ⁵³ The cost of implementation on a larger scale could be prohibitive particularly for certain types of therapy such as injectable buprenorphine.^46,67 For programs that received federal funding, additional restrictions on practices such as purchasing syringes for syringe exchange could limit harm reduction. ³⁸ Additionally, the novelty of some programs^38,53 made it difficult to navigate licensing and credentialing regulations. At a more local level, programs were often vulnerable to community resistance. Some mobile units noted being asked by the community and/or law enforcement agencies to relocate or described clients being questioned by the police.^38,66 Clients for the mobile program described in Pepin et al were displaced by law enforcement sweeps of homeless encampments. ⁶⁰  The treatment progress for clients involved with the criminal legal system (CLS) can be disrupted during periods of incarceration. ⁷⁰  While some CLS systems maintain treatment during incarceration and transition clients into care post-incarceration, this is not always the case. Even more, in Krawczyk et al, a program tailored to these clients, the disorganized nature of the local CLS itself precluded transitions into care. ⁵⁴

Internal Barriers to Implementation

Some mobile programs were constrained by their physical space, creating concerns about client privacy and limiting both the number of clients that could be seen and the type of services offered (eg, urine drug tests).^64,66 Due to the small physical space of a mobile unit, the program in Hoffman et al noted that clients with disabilities may have difficulty accessing services. ⁵¹ Depending on location, mobile programs also faced decreased engagement due to inclement weather.^38,51,64 Although the services offered by the types of programs varied, many were unable to meet clients’ full mental health or social needs.^24,70 If additional services were available and offered, the cost was higher as compared to typical primary care. ⁶⁶ Programs reported staffing shortages and turnover as ongoing barriers, and some programs noted difficulty recruiting and retaining medical providers who were comfortable with providing a harm reduction approach over other treatment modalities.^24,38,46

Individual Barriers to Implementation

At the individual level, programs frequently had to overcome client hesitancy to engage, which was often noted as resulting from previous trauma and stigma when seeking health care.^42,60 Some patients found the specific communities in which mobile units were located were triggers and a barrier for further engagement.^57,70 Clients’ socioeconomic stability also complicated the enrollment procedures with several programs citing homelessness, lack of insurance, and lack of reliable communication (no phone) as hurdles to overcome.^{24,52,54,57,58}

Facilitators to Implementation

External Facilitators to Implementation

Partnering with stakeholders at all levels was key. Community buy-in was facilitated through engagement with local or tribal leaders.^40,51,53 Public health departments, local government, community leaders, and existing service organizations (ie, shelters) helped programs target hotspot areas,^38,61,66 establish client trust, and facilitate care coordination.^38,46,66 Programs also recognized pharmacies as being instrumental in their success, such as pharmacists who demonstrated a destigmatizing approach and/or were flexible for clients who did not have state-issued identification cards.^24,38,53,54 Del Pozo et al and Krawczyk et al noted support from law enforcement agencies, either by directly engaging clients involved with the criminal legal system or by reframing their own approach to policing.^40,54 Several programs identified funding from local government and agencies as critical for operations and/or to provide free buprenorphine to clients.^{19,37,39,49,60}

Internal Facilitators to Implementation

To better engage their target population, several programs co-located with existing service organizations. Mobile programs benefited from operating near existing service organizations such as SSPs, community nonprofits, or food pantries, including having access to parking.^48,60,66 Other programs took advantage of the physical infrastructure and workflow of these existing service organizations by co-locating in the organizations’ office space.^{22,24,40,52,53,57,72} Beyond the physical infrastructure, each program’s harm reduction approach offered a welcoming and non-stigmatizing environment for patients.^{38,42,44,48,51}

Individual Facilitators to Implementation

Staff experience varied among programs. Staff members with lived experience served as peer or recovery coaches, connecting with and serving as liaisons for clients.^{37,38,45,46,57,58} Programs were often intentional in hiring staff from within the same community to provide culturally competent care.^38,51 Case managers, coordinators, and social workers were cited as being instrumental in helping clients navigate treatment and address needs beyond MOUD management.^24,66 In Regis et al, the program specifically hired harm reduction specialists who could provide additional counseling. ⁶¹ The most common source of referral was client to client word-of-mouth, which fostered trust among program participants.^19,38

Service and Clinical Outcomes

Of the 41 studies, 11 reported 30-day (or “one month”) retention as a quantitative outcome, prompting researchers to select this time point since it was the most reported across studies. The second most frequently reported time point for outcome-reporting measures was 90 days (or 3 months) after treatment initiation, with 10 of 41 studies reporting an outcome. Retention outcomes are summarized in Table 3.

Table 3.

Program Retention Outcomes. Among the 41 studies, eleven programs published retention outcomes, with the most commonly-reported outcome being the percentage of patients retained at one month.

Program type	Study	Program name	Location	Patient population	Retention in care definition	One month retention outcome (%)	Other retention outcomes	Adverse events
Syringe Service Program	Jakubowski 2022	Unnamed	New York City, NY, USA	118 participants receiving buprenorphine prescriptions from an SSP-based buprenorphine program	1. Time in treatment during the first treatment episode 2. Total percentage of days “covered” with a buprenorphine prescription during the first 180 d of treatment	62	1. Retention at 90 d: 43% 2. Retention at 180 d: 31% 3. Total percentage of days covered with a buprenorphine prescription during the first 180 d of treatment (43% with an IQR of 8-92%).	None reported
Syringe Service Program	Gadomski 2023	The Mountain Center	Espanola, NM, USA	137 individuals seeking buprenorphine prescription from the harm reduction clinic	Not defined	33.65	1. Retention rate in care at 1 mo: 33.65% (35/104) 2. Retention rate in care at 3 mo: 29.41% (25/85) 3. Retention rate in care at 6 mo was 31.15% (19/61) 4. Percent of patients who visited the clinic only once: 40.88% 5. Percent of patients who returned to clinic for at least one visit: 59.12%	Not reported
Mobile program	Krawczyk 2019	Project Connections at Re-Entry (PCARE)	Baltimore, MD, USA	190 individuals seen outside the Baltimore City Jail, referred by staff or walk in	4 continuous weeks of appointments	31.6	129/190 patients (67.9%) returned for a second visit or more. On average, patients who returned for a second visit or more were involved in treatment for 8 wk.	Not reported
Mobile program	Selitsky 2023	Project Connections at Re-Entry (PCARE)	Baltimore, MD, USA	566 participants who received buprenorphine from the PCARE van outside the jail	Retention reported by dose of buprenorphine. 1. 30 d retention: engagement with buprenorphine treatment (presented for visits, received rx) for 30 d or more since their initial intake date 2. 90 d retention: engagement with buprenorphine treatment (presented for visits, received rx) for 90 d or more since their initial intake date	93.8 (average between 16 mg and >16 mg groups)	1. 90 d retention: 16 mg group (67.6%), >16 mg group (82.7%) 2. Greater odds of 30 d retention if daily dose >16 mg	None
Mobile program	O’Gurek 2021	Begin the Turn	Philadelphia, PA, USA	147 individuals receiving care from the multidisciplinary mobile care unit	1 mo definition: a visit for buprenorphine had to take place at or after the individual was part of the program for 1 mo, requiring that a visit for buprenorphine occurred during the preceding week. 3 and 5 mo definition: a visit for buprenorphine	61.2	1. Retention at 3 mo: 36.6% 2. Retention at 5 mo: 27.6%	Not reported
Mobile program	Rosecrans 2022	The Spot	Baltimore, MD, USA	421 individuals seen by the mobile unit in Baltimore, MD	Received a buprenorphine prescription between 91and 106 d, regardless of prior lapses in treatment of any length	56	Retention in buprenorphine treatment at 3 mo: 26.9%	Not reported
Street medicine	Henriksen 2018	Low Threshold Substitution Treatment in Oslo	Oslo, Norway	331 patients who completed at least one buprenorphine induction	Total time on medication (4 consecutive days without medication required a new induction attempt and was registered as a new treatment episode)	52	1. Number of patients that completed at least 1 induction (4-29 d of treatment): 282/331 2. Average treatment length: 111.4 d 3. Number of patients considered to be stabilized (>29 d of treatment): 171/331 4. Average treatment length: 164.9 d 5. Average number of induction attempts per participant (overall): 3.9 6. Average number of induction attempts per male participant: 4 7. Average number of induction attempts per female participant: 3.6	2 patients reported adverse reactions (one had generalized allergic dermatological reaction and the other developed hypotension requiring hospitalization)
Street medicine	Carter 2019	San Francisco Street Medicine	San Francisco, CA, USA	95 individuals receiving at least one buprenorphine prescription from program, target population is people experiencing homelessness with OUD	More than 2 wk of active buprenorphine prescription during the month	37	1. 3  mo retention: 27% 2. 6 mo retention: 27% 3. 9 mo retention: 26% 4. 12 mo retention: 18%	1. Number of deaths from fentanyl and methamphetamine overdose: 1 2. Number of patients who received emergency or inpatient medical treatment for opioid overdose requiring naloxone: 4 3. Number of patients treated for possible opioid overdose not requiring naloxone: 5
Street medicine	Gibson 2023	The Connecticut Mental Health Center	New Haven, CT, USA	6 patients for whom buprenorphine was prescribed	Not defined	83	1. 3/6 patients engaged in the program for >3 mo 2. 2/6 patients engaged in the program for >6 mo 3. Average number of encounters per week: 1.1 4. Average total number of prescriptions: 9.5	Not reported
Other: Pharmacy-based	Green 2023	Unnamed (pharmacy integrated)	Providence, RI, USA	100 individuals who obtained care at one of 3 pharmacies and received buprenorphine	Participants who received follow-up care at 1 mo after randomization	89	Patients who attended follow-up care at usual medical site: 5/30 (17%)	During the first month, 3 nonfatal overdoses occurred (one of which was in the pharmacy group) and 3 non-overdose-related opioid emergency department visits occurred (2 of which were in the pharmacy group)
Other: Hepatitis C Treatment Center	Hill 2022	ANCHOR	Washington, DC, USA	67 patients receiving HCV treatment not on opioid agonist therapy	Retention at 1 mo defined as active buprenorphine prescription at day 30. Retention at 6 and 12 mo defined as active buprenorphine prescription within 7 d of those timepoints.	60	Retention, n (% total participants, % total participants that initiated treatment): at 1 mo—40 (60%, 82%), at 6 mo—32 (48%, 65%), at 12 mo—29 (43%, 59%).	2 patients (10%) died during first year of treatment

A few studies assessed non-buprenorphine-related aspects of care relevant to OUD recovery in their primary outcomes. Notably, Stewart et al chose to focus on pregnancy, Human Immunodeficiency Virus (HIV), HCV, and sexually-transmitted infection testing and treatment outcomes on a program serving women living unhoused and engaging in transactional sex work in North Seattle, WA. ⁶⁶ Del Pozo et al summarized opioid overdose deaths in communities engaging with CommunityStat, a public health intervention to reduce opioid overdose deaths in Burlington, VT from 2017 to 2020. ⁴⁰ This study showed a 50% reduction in fatal overdoses in the county compared to a 20% increase in fatal overdoses in the remaining VT counties during the same period. Yet another study, described in Fixler et al, reported average drug, non-drug, and total arrests in populations served by a Prevention Point Pittsburgh (PPP) clinic in Pittsburgh, PA compared to areas not served by a clinic. Compared to populations living farther than 1 mile from a clinic, arrests fell by 34.13%. ⁴³

Discussion

Models of Care and Key Components of Programs

This scoping review presents a current and comprehensive review of the literature on low-threshold buprenorphine programs in nontraditional settings. Most programs highlighted all 4 principles of low-threshold buprenorphine treatment as defined by Jakubowski and Fox, including harm reduction, same-day start, flexibility, and location in areas where people who use opioids are likely to frequent. ¹⁶ However, as the included studies range in publication date from 2010 to 2024, and the acceptance and terminology of low-threshold treatment modalities has changed over this timeframe, holding a program published 15 years ago to the same standard as 1 in recent years is not considering the appropriate context given the changing regulation and practice norms. We assessed the context and publication dates of programs that may have not explicitly been described as low-threshold. Stancliff 2012, for instance, was published at a time when low-threshold programs were less well-described and widely utilized across the country than in more recent years. It fits the picture of a low-threshold program in that it was in a setting where individuals with OUD frequently spend time, no patients were penalized for adherence or positive drug tests, and thus was included in this review.

Given that the needs and preferences of people who use drugs may vary across countries and cultures, it is important to note that most (36 or the 41) of the programs described were in the United States. Regulatory requirements regarding buprenorphine prescription varies across countries. For instance, in India, OUD agonist treatment can only be given by government-run organizations and AIDS-based non-government organizations. ⁷³ Alternatively, some countries have been utilizing low-threshold principles for many years. As an example, France started prescribing buprenorphine in 1996 with no additional training requirements for prescribers and no specific urine screening requirements for patients, which has resulted in a nationwide decrease in opioid overdose rates. ⁷³

Additionally, there are aspects of low-barrier programs that require further exploration. For example, most low-barrier programs offer but do not require engagement in therapy or other behavioral health services; however, this was not standard across all programs. An instance of this is the Tringale 2015 study which described itself as low-threshold within a needle exchange but required peer support group participation. This may reflect the evolving understanding across the last 10 years of what low-threshold means, as the most recent programs did not require therapy or peer support group inclusion, and align with the most up-to-date SAHMSA guidance on low-barrier models of care for substance use disorders. ⁷⁴

Competing Priorities: Diversion Prevention Versus Removing Barriers to Care

When considering what requirements to place on clients, low-threshold programs should carefully consider whether the benefit to the client justifies the burden placed on them, especially for requirements that may be stigmatizing. ⁷⁵ One example is the urine drug test used to assess if clients are taking or diverting their buprenorphine prescriptions. While it is often in a program’s best interest to minimize diversion risk, the evidence is mixed regarding the harm versus benefit of diverted buprenorphine to the true stakeholders in this discussion: people who use drugs. Most people who use non-prescribed buprenorphine do so for the same reasons for which it is prescribed: to manage opioid withdrawal symptoms or achieve/maintain abstinence from other opioids. ⁷⁶ Such use of non-prescribed buprenorphine can act as a “bridge” to a treatment program and can be predictive of longer engagement in treatment. One study found that clients with prior use of non-prescribed buprenorphine were twice as likely to be retained in treatment for 6 months compared to those without. In many cases where the use of non-prescribed buprenorphine replaces substances with a high likelihood of fentanyl contamination, diversion may even prevent overdose deaths in people who may not engage with the healthcare setting. ⁷⁷ Adams et al simulated various rates of buprenorphine diversion in the population of people who use drugs in North Carolina and found that increased rates of diversion in their model decreased opioid deaths by up to 5%. ⁷⁸ Further, the 5 programs that do not require or use urine drug test results serve as evidence that drug testing is not essential to all low-threshold buprenorphine programs. Collectively, these data pose an important question for developing programs—how much should programs weigh diversion concerns against developing as accessible a program as possible?

Determinants of Implementation

Among the studies reviewed, relationships with community stakeholders were found to be critical to program implementation. This is consistent with prior studies showing the importance of engaging with community leaders and local government to obtain support and buy-in. ⁷⁹ Public health departments, in addition to local government, may be able to provide data on drug use and overdose hotspot locations for targeting outreach or mobile services. Collaboration with other organizations (SSPs, shelters, food pantries, community centers) serving the same population can also facilitate patient recruitment. Engaging with law enforcement may be more challenging given philosophical differences in OUD treatment ⁸⁰ ; however, attempts should be made to communicate program objectives and plans including significant advocacy for clients with CLS involvement to eliminate interruptions to treatment during incarceration or probation periods. For programs that do not dispense MOUD directly, establishing a network of pharmacies is also imperative. Identifying pharmacies that both stock MOUD and will be flexible regarding patient identification can greatly minimize barriers for patients.

Patients’ diverse needs were an important consideration for programs. The population served by low-threshold programs often faces homelessness and lack of employment, insurance, transportation, and/or access to communication. While not essential to implementing a low-threshold program, providing additional services may increase recruitment and retention although the cost of wraparound services may prove prohibitive to some programs without additional funding. Future research is needed to evaluate the cost-effectiveness of low-threshold programs and identify sustainable funding sources. ⁸¹

Local attitudes about harm reduction were sometimes noted as a barrier. It is well documented that stigma is pervasive among both clients and providers and can be a significant barrier to care.^82,83 Stigma within communities can lead to friction with local stakeholders. For programs, this can hinder recruitment of both patients and providers. Programs with a more flexible harm reduction approach may also find themselves at odds with OUD treatment programs in their communities implementing more traditional methods.

Program Outcomes

This review demonstrates the growing acceptance of low-barrier buprenorphine in non-traditional settings, and that many new delivery models are emerging. Such rapid innovation, however, has caused a lag in the development of standardized program outcomes and measures of success.

Although the most commonly-reported outcome was retention in treatment, we found that the definition of retention varied widely. For many low-threshold programs prioritizing a harm reduction approach, there is a focus on meeting individuals where they are in treatment and providing care to clients regardless of their consistency. The nature of this approach and the instability of many clients’ support structures means clients come in and out of care frequently, making “retention” difficult to define. Ly et al defined 3-month retention as clients having a prescription for 80% of days during a 3-month period. ⁵⁶ Bachhuber et al defined clients as retained if they had no 60-day period without a prescription or appointment and had not been administratively discharged. ⁷² Hill et al defined 6-month and 12-month retention as having an active prescription within 7 days of those timepoints, regardless of any lapses in treatment. ²² Carter et al defined a client as having been retained in care for any given month if they had an active prescription for 2 weeks during that month. ³⁷ Such widely differing definitions make comparison of retention rates difficult and any meta-analysis nearly impossible.

As new programs seek to use evidence-based practices in designing their services, the literature would benefit from a unified definition of retention. A generally accepted measure of minimally adequate MOUD retention is incorporated in a measure of pharmacotherapy retention recently endorsed by the National Quality Forum (NQF #3175), which specifies that patients initiating a medication such as buprenorphine should be continuously retained for a minimum of 6 months. ⁸⁴ However, given the unique population served by low-threshold programs, this retention definition may be too stringent. Reporting the percentage of days with an active buprenorphine prescription may provide more valuable insight. When interpreting retention rates, it is important to note that retention rates are most valuable in their ability to serve as an intermediary outcome associated with more important outcomes such as decreased all-cause mortality. ⁹ Retention can be simpler to report because it can be objectively determined from a chart review, but when possible, further research should include measures of recovery capital, which encompasses the internal and external resources that can be drawn upon to initiate and sustain recovery such as employment status, housing status, and quality of life. ⁸⁵ A recent e-Delphi consensus study proposes an opioid use disorder core outcomes set for OUD treatment efficacy and effectiveness research. ⁸⁶ The core outcomes set captures 5 OUD treatment outcomes: 2 patient-reported (global impression of improvement and incident non-fatal overdose); 1 clinician-reported (illicit/non-medical drug toxicology); and 2 from administrative records (duration of treatment and fatal opioid poisoning). Utilizing this type of core outcomes set to evaluate non-traditional OUD treatment programs may provide a more multidimensional and standardized picture of novel models of care.

For programs centered in harm reduction, treatment is not the goal of many participants who engage in the program; therefore, broader outcome measures such as participant engagement in services or successful connection to resources may be more appropriate. Further research is needed to identify the outcomes that are a priority for people who use drugs, and to develop effective strategies of program implementation directed toward the goals of clients rather than goals imposed on them by the healthcare system. This would illuminate the value of services that programs offer outside of buprenorphine prescriptions and provide evidence to expand these services to offer holistic, patient-centered support.

Limitations

The design of this review led to several limitations in its ability to provide a scope of the low-threshold MOUD landscape. Primarily, the study excluded any programs that did not prescribe buprenorphine, as low-threshold approaches to methadone are often more challenging to implement due to dispensing regulations. The study also only included programs that were highlighted in peer-reviewed articles, likely causing us to miss novel programs or those not described in peer-reviewed literature. An integrative review in the future which includes additional literature would be useful to capture the wide range of program types. Further, in other countries with different barriers to treatment, programs that meet the definition of low-threshold may not be novel enough to be considered for publication, which may contribute to the over-representation of U.S. based studies in this sample. Lastly, there are a variety of terms in use to mean “low-threshold,” and some programs that would otherwise qualify for inclusion in our study may not have used such language at all or may not have been widely available in English, thus were not captured by our search terms.

Future Directions

There are several gaps in the literature, especially regarding outcome reporting. Future research is needed to identify what outcomes are most important to people who use drugs, who are the true stakeholders of low-threshold MOUD programs. To the degree that retention is determined to be an important outcome, a more unified definition of retention is essential to be able to analyze what aspects of programs promote or inhibit retention. Furthermore, the field must develop effective ways of measuring recovery capital as reportable outcomes. There is also value in studying the components of low-threshold MOUD programs that have the greatest impact on MOUD retention, reduced morbidity, and reduced mortality. Finally, more studies are needed to examine how novel program designs fit the needs of each unique community.

Conclusion

Low-threshold buprenorphine programs are an innovative way to bring OUD treatment to people who otherwise may not engage in care. As a scoping review, we have identified a high level of heterogeneity in program structure, which is to be expected considering the rapidly changing treatment landscape and differences by geographical location. However, such heterogeneity poses challenges in standardized program reporting and takeaway points for persons looking to develop a program in a new community. Despite such program variety, a few common types emerged: syringe service programs, mobile programs, community center programs, and street medicine programs. Most programs prioritize the 4 key principles of low-threshold treatment: (1) a harm reduction approach, (2) same-day treatment entry, (3) flexibility, and (4) wide availability in places frequented by people with opioid use disorder. Additionally, most programs emphasized community partnerships as key facilitators of implementation and noted that expanded funding is still desperately needed to support recovery holistically. Retention in care is the most frequently reported outcome; however, because it is difficult to define in low-threshold settings, definitions vary widely. Future efforts should determine which outcomes are most important to people who use drugs and standardize those outcome measurements to assess current program success and inform future program development.